JPH0836198A - High peak power wavelength-converted pulse laser device - Google Patents

Abstract

PURPOSE:To improve the peak power conversion efficiency and output stability of wavelength-converted laser beam by nonlinear optical crystal. CONSTITUTION:Exciting pulse laser beam becomes becomes short in pulse width by being transmitted through a breakdown medium 10 and is made incident on nonlinear optical crystal 3 to generate pulse lash with different wavelength. Thus, the exciting laser beam with higher and higher peak intensity can be made incident as the pulse width of the exciting pulse laser beam made incident on the nonlinear optical crystal 3 is shorter and shorter, and the peak intensity of obtained wavelength-converted pulse laser beam becomes high as a result, thereby reducing the damage to the nonlinear optical crystal 3 by as much as the energy made incident on the nonlinear optical crystal 3 is small.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high peak power wavelength conversion pulsed laser device which performs wavelength conversion using a nonlinear optical crystal.

[0002]

2. Description of the Related Art FIG. 7 is a block diagram of a wavelength conversion pulsed laser device. The excitation pulsed laser light output from the laser light generator 1 is focused by the condensing optical system 2 including a lens or the like to increase the intensity and is incident on the nonlinear optical crystal 3.

The non-linear optical crystal 3 generates laser light having different wavelengths upon incidence of the pump pulse laser light, for example, converted pulse laser light having a wavelength ω1 to a wavelength ω2 of the pump pulse laser light.

Here, the pulsed laser light whose wavelength has been converted by the nonlinear optical crystal 3 has a wavelength ω1 of the original pump pulsed laser light that has not been converted and a wavelength ω2 of the converted laser light.
And are mixed.

For this reason, the pulse laser light wavelength-converted by the nonlinear optical crystal 3 is separated by the beam splitter 4 into laser light of wavelength ω1 and laser light of wavelength ω2. The wavelength ω2 converted by the nonlinear optical crystal 3
As a method of separating the laser light of (or ω3), the method shown in FIG.
In some cases, a plurality of mirrors having appropriate reflection characteristics, for example, an input mirror 5 and an output mirror 6 are arranged on the incident side and the emitting side of the nonlinear optical crystal 3 as shown in FIG. The efficiency η when converting the excitation pulsed laser light into different wavelengths has the following relationship with respect to the peak power.

[0006]

[Equation 1]

As can be seen from this equation, the efficiency η monotonically increases with the increase of the intensity Io of the pump pulse laser. Therefore, in order to increase the conversion efficiency η, it is necessary to increase the intensity Io as much as possible. As the strength Io increases, the efficiency η
Becomes close to 1 and can be converted in principle close to 100%.

However, the intensity of the pump pulse laser beam that can actually enter the nonlinear optical crystal 3 is limited by the damage limit that does not damage the nonlinear optical crystal 3. As a result, the peak power of the laser light converted by the nonlinear optical crystal 3 is also limited to the value corresponding to the pump pulse laser light at the damage limit in the above formula (1).

Further, since the peak power of the pulsed laser light wavelength-converted by the nonlinear optical crystal 3 is proportional to almost the square of the peak power of the pumped pulsed laser light, the output value of the pumped pulsed laser light varies from pulse to pulse. In this case, the output fluctuation of the laser light whose wavelength has been converted is also emphasized by its square and becomes unstable.

[0010]

As described above, the pulsed laser light whose wavelength is converted by the nonlinear optical crystal 3 generally has much lower peak power than that of the pumped pulsed laser light, and its output becomes unstable. This is a bottleneck when applied to applications such as processing.

Therefore, an object of the present invention is to provide a high peak power wavelength conversion pulsed laser device in which the peak power conversion efficiency and output stability of the wavelength conversion laser light by the nonlinear optical crystal 3 are improved.

[0012]

According to a first aspect of the present invention, there is provided a high peak power wavelength conversion pulsed laser device for injecting pump laser light into a nonlinear optical crystal to generate pulsed laser light having different wavelengths. This is a high peak power wavelength conversion pulsed laser device in which an optical breakdown medium for pumping laser light is arranged on the incident side to achieve the above object.

According to a second aspect of the present invention, in a high peak power wavelength conversion pulsed laser device for injecting pump laser light into a nonlinear optical crystal to generate pulsed laser light having different wavelengths, the pumping laser arranged on the incident side of the nonlinear optical crystal is used. An optical breakdown medium for the laser light, an input mirror arranged on the incident side of the breakdown medium to collect the pumped laser light to enter the breakdown medium, and an input mirror arranged on the emission side of the breakdown medium. A high peak power wavelength conversion pulsed laser device, which is provided with a collimator lens for returning light emitted from a breakdown medium to parallel light, and which is intended to achieve the above object.

According to the third aspect, the breakdown medium is at least air, N ₂ or He gas. According to the fourth aspect, the breakdown medium adjusts the breakdown intensity for the pump laser light at least by the gas pressure. According to the fifth aspect, the spatial filter is arranged at the focusing point of the excitation laser light in the breakdown medium.

[0015]

According to the first aspect of the present invention, the pump laser light is transmitted through the breakdown medium to have its pulse width shortened and enters the nonlinear optical crystal to generate laser lights of different wavelengths.

As described above, the shorter the pulse width of the pumping laser light that is incident on the nonlinear optical crystal, the more the pumping laser light having a high peak intensity can be made incident, and the peak intensity of the resulting wavelength-converted laser light is also high. In addition, damage to the nonlinear optical crystal can be reduced by the amount of energy that is incident on the nonlinear optical crystal.

According to the second aspect, the pump laser light is focused by the input mirror and enters the breakdown medium,
By passing through this breakdown medium, the pulse width is shortened, converted into parallel light by the collimator lens, and incident on the nonlinear optical crystal. Then, laser lights of different wavelengths are generated by this nonlinear optical crystal.

According to the third aspect, at least the gas of air, N ₂ or He is used as the breakdown medium to shorten the pulse width of the pump laser light. According to the fourth aspect, the breakdown strength of the breakdown medium with respect to the excitation laser light is adjusted by at least the gas pressure.

According to the fifth aspect, by disposing the spatial filter at the condensing point of the pump laser light in the breakdown medium, the spatial frequency component which does not contribute to the wavelength conversion is removed at the same time, and the life of the nonlinear optical crystal is reduced. Can be long

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to the drawings. The same parts as those in FIG. 7 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 1 is a block diagram of a high peak power wavelength conversion pulsed laser device.

An optical breakdown medium 10 is arranged on the laser light path between the laser light generator 1 and the nonlinear optical crystal 3. The breakdown medium 10 is enclosed in a medium container 11. The container 11 is provided with an entrance window 12 and an exit window 13 on the surfaces facing each other.

The breakdown medium 10 has the function of shortening the pulse width of the incident pump pulse laser light and outputting the threshold voltage for the breakdown to be substantially constant.

The breakdown medium 10 is specifically air or a gas such as N ₂ or He. Further, the strength of the breakdown caused by the breakdown medium 10 is a function of the type of medium and gas pressure, and is adjusted by this gas pressure.

A short focus lens 14 is arranged on the incident side of the breakdown medium 10, and a collimator lens 15 is arranged on the emission side of the breakdown medium 10. Next, the operation of the apparatus configured as described above will be described.

The excitation pulsed laser light output from the laser light generator 1 is focused by the short focus lens 14 and enters the breakdown medium 10 through the entrance window 12 of the container 11.

In this breakdown medium 10, when breakdown occurs at a certain intensity of the pump pulse laser light,
Plasma is generated and a shield effect occurs, and the subsequent excitation pulsed laser light is blocked.

As a result, the excitation pulsed laser light is emitted as shown in FIG.
As shown in (a), the peak intensity is slightly reduced, but the pulse width is very short from t1 to t2. This pulse width is generally less than half.

Further, as shown in FIGS. 2 (a) and 2 (b), the threshold value at which breakdown occurs is substantially constant even if the peak intensities of the pump pulse laser light are different. Thereby, even if the output value of the pump pulse laser light fluctuates, the peak intensity of the pump pulse laser light emitted from the breakdown medium 10 becomes substantially constant.

As described above, the excitation pulsed laser light is transmitted through the breakdown medium 10 so that the pulse width becomes shorter and the peak intensity becomes constant, which is returned to parallel light by the collimator lens 15 and enters the nonlinear optical crystal 3. .

The non-linear optical crystal 3 generates laser light having different wavelengths upon incidence of the pump pulse laser light, for example, pulse laser light having a wavelength ω1 to a wavelength ω2 of the pump pulse laser light.

Since the pulsed laser light wavelength-converted by the nonlinear optical crystal 3 contains the wavelength ω1 of the original excitation pulsed laser light which is not wavelength-converted and the wavelength ω2 of the converted pulsed laser light, the beam The splitter 4 splits the pulsed laser light of wavelength ω1 and the pulsed laser light of wavelength ω2.

The damage limit of the nonlinear optical crystal 3 depends on the energy of the pump pulse laser light incident per unit area, although it depends on the type of the nonlinear optical crystal 3.

That is, as shown in FIGS. 3 (a) and 3 (b), when the damage limit energy (hatched portion in the figure) is incident on the nonlinear optical crystal 3 in a unit area, the pulse width of the pump pulse laser light is increased. The shorter is, the higher the excitation pulsed laser light having a high peak intensity can be incident on the nonlinear optical crystal 3.

As a result, the peak intensity of the wavelength-converted pulsed laser light obtained by the nonlinear optical crystal 3 becomes high. Further, as shown in FIG. 4, when the excitation pulse laser lights E1 and E2 having different pulse widths are used, if the peak intensities of the excitation pulse laser lights E1 and E2 are the same, the wavelength of the nonlinear optical crystal 3 is increased. The peak intensities of the pulsed laser lights obtained by the conversion become equal, but in these pumped pulsed laser lights, the nonlinear optical crystal 3
Since the shorter the pulse width of the incident energy is, the damage to the nonlinear optical crystal 3 is reduced accordingly, and the life of the nonlinear optical crystal 3 can be extended.

For example, when the pulse width of the pump pulse laser light is 50 nsec and the peak intensity is 10 MW / cm ² , the damage limit of the nonlinear optical crystal 3 is 25 MW for the pump pulse laser light having the pulse width 20 nsec. /
It will be about cm ² .

The energy from the excitation pulsed laser light is
For example, 100 mJ, beam area of excitation pulsed laser light 1
If cm ² is given, the peak intensity I becomes I = 100 mJ / 50 nsec · 1 cm ² = 2 MW / cm ² (2). Therefore, if the maximum conversion efficiency η is to be obtained, the pump pulse laser beam Focusing may be performed so that the area becomes 1/5.

If the conversion efficiency η at this time is 10%,
The energy of the pulsed laser light wavelength-converted by the nonlinear optical crystal 3 is 100 mJ · 0.1 = 10 mJ (3), and the pulse width is

[0038]

[Equation 2] And the peak power is

[0039]

(Equation 3) Becomes

On the other hand, in the case of the device of the present invention, the breakdown of the breakdown medium 10 causes the excitation pulse laser light to have, for example, a pulse width of 20 nsec and an energy of 30.
When it becomes mJ, the peak intensity I becomes I = 30 mJ / 20 nsec.1 cm ² = 1.5 MW / cm ² (6).

Thus, the peak intensity I (1.5 MW / cm
² ) is reduced as compared with the peak intensity I (2 MW / cm ² ) without the breakdown medium 10, but the damage limit is about 25 MW / cm ^{2 as} described above, so the maximum conversion efficiency η is obtained. The beam area of the pump pulse laser light is

[0042]

[Equation 4] Can be made as small as possible.

Since the conversion efficiency η at this time is about 20%, the energy of the wavelength-converted pulse laser light is 30 × 0.2 = 6 mJ (8) The pulse width is

[0044]

(Equation 5) Becomes Therefore, the energy of the wavelength-converted laser light is small, but the peak power P is

[0045]

(Equation 6) And become bigger.

As described above, in the first embodiment,
The pumping pulsed laser light is focused by the input mirror 14 to enter the breakdown medium 10, and the pulse width is shortened by passing through the breakdown medium 10 to enter the nonlinear optical crystal 3. The nonlinear optical crystal 3 Since the pulsed laser light having different wavelengths is generated by the above, the shorter the pulse width of the pumped pulsed laser light that enters the nonlinear optical crystal 3, the more the pumped laser light having a higher peak intensity can be made to enter, and the resulting wavelength conversion The peak intensity of the generated laser light is also increased, and the amount of energy incident on the nonlinear optical crystal 3 is small, so that damage to the nonlinear optical crystal 3 can be reduced and the life can be extended.

The threshold at which breakdown occurs is
Even if the peak intensity of the pumping pulse laser light is different, it becomes almost constant. Therefore, even if the output value of the pumping pulse laser light fluctuates, the peak intensity of the pumping pulse laser light emitted from the breakdown medium 10 becomes almost constant. it can. As a result, it can be applied to applications such as laser processing.

Further, by adjusting the gas pressure of the breakdown medium 10 enclosed in the container 11, the converted wavelength can be adjusted to extract the desired wavelength. (2) Next, a second embodiment of the present invention will be described. The same parts as those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

FIG. 5 is a block diagram of a high peak power wavelength conversion pulsed laser device. A pinhole 20 as a spatial filter is arranged at the focus position of the excitation pulsed laser light in the container 11 that encloses the breakdown medium 10.

The pinhole 20 has a function of removing a spatial frequency component that does not contribute to wavelength conversion. With such a configuration, the pump pulse laser light output from the laser light generator 1 is focused by the short focus lens 14 and enters the breakdown medium 10.

In this breakdown medium 10, when breakdown occurs at a certain intensity of the pump pulse laser light,
Plasma is generated and a shield effect occurs, and the subsequent excitation pulsed laser light is blocked.

As a result, the peak intensity of the pump pulse laser light is slightly reduced as described above, but the pulse width thereof is extremely short. Further, the excitation pulsed laser light passes through the pinhole 20 to remove the spatial harmonic component that does not contribute to wavelength conversion.

As described above, the pumping pulsed laser light is transmitted through the breakdown medium 10 so that the pulse width becomes shorter and the peak intensity becomes constant, and the spatial harmonic components that do not contribute to the wavelength conversion are removed. Is converted into parallel light by and enters the nonlinear optical crystal 3.

The non-linear optical crystal 3 generates laser light having different wavelengths depending on the incidence of the excitation pulse laser light, for example, pulse laser light having a wavelength ω1 to a wavelength ω2 of the excitation pulse laser light.

Here, FIG. 6 shows the divergence angle of the pump pulse laser light that passes through the nonlinear optical crystal 3, and when the pump pulse laser light passes through the pinhole 20,
The spread angle becomes smaller.

Accordingly, when the phase matching tolerance angle of the nonlinear optical crystal 3 is small, it is optimal to pass the pump pulse laser light through the pinhole 20 to reduce the spread angle of the pump pulse laser light.

That is, when the phase matching allowable angle of the nonlinear optical crystal 3 is small and the divergence angle of the pump pulse laser light is large, a spatial harmonic component that does not contribute to wavelength conversion is incident and the extra component is wavelength converted. Because it does.

The laser light after passing through the nonlinear optical crystal 3 is separated by the beam splitter 4 into a laser light of wavelength ω1 and a pulse laser light of wavelength ω2. As described above, in the second embodiment, since the pinhole 20 is arranged at the focal position of the excitation pulsed laser light in the breakdown medium 10, in addition to the effect of the first embodiment, the phase of the nonlinear optical crystal 3 is increased. When the matching tolerance angle is small, spatial harmonic components that do not contribute to wavelength conversion, which is a problem, can be removed, and the life of the nonlinear optical crystal 3 can be extended.

The present invention is not limited to the above embodiments, but may be modified as follows. For example, as a method for separating the laser light of each wavelength converted by the nonlinear optical crystal 3, a plurality of mirrors having appropriate reflection characteristics on the incident side and the emitting side of the nonlinear optical crystal 3, for example, shown in FIG. An optical resonator may be constructed by arranging the input mirror 5 and the output mirror 6.

[0060]

As described above in detail, according to the present invention, it is possible to provide a high peak power wavelength conversion pulsed laser device with improved peak power conversion efficiency and output stability of wavelength conversion laser light by the nonlinear optical crystal 3.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a first embodiment of a high peak power wavelength conversion pulsed laser device according to the present invention.

FIG. 2 is a diagram showing a pulse waveform when a breakdown is caused by a breakdown medium.

FIG. 3 is a waveform diagram of each wavelength conversion light with respect to each pump pulse laser light having a different pulse width.

FIG. 4 is a waveform diagram of each wavelength-converted light with respect to each pump pulse laser light having the same peak intensity but different pulse widths.

FIG. 5 is a configuration diagram showing a second embodiment of a high peak power wavelength conversion pulsed laser device according to the present invention.

FIG. 6 is a diagram showing a divergence angle of a pump pulse laser beam.

FIG. 7 is a configuration diagram of a conventional wavelength conversion pulsed laser device.

FIG. 8 is a configuration diagram of a conventional wavelength conversion pulsed laser device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Laser light generator, 3 ... Nonlinear optical crystal, 10 ... Breakdown medium, 11 ... Medium container, 12 ... Incident window, 13 ... Exit window, 14 ... Short focus lens, 15 ... Collimating lens.

Claims (5)

[Claims] 1. A high peak power wavelength conversion pulsed laser device for generating pump laser light having different wavelengths by making pumping laser light incident on a nonlinear optical crystal, wherein the pumping laser light is optically incident on the incident side of the nonlinear optical crystal. High peak power wavelength conversion pulsed laser device characterized by arranging various breakdown media. 2. A high peak power wavelength conversion pulsed laser device for generating pulsed laser light having different wavelengths by making pumping laser light incident on a nonlinear optical crystal, wherein the pumping laser light is arranged on the incident side of the nonlinear optical crystal. An optical breakdown medium, an input mirror arranged on the incident side of the breakdown medium to collect the excitation laser light and make it enter the breakdown medium, and an input mirror arranged on the emission side of the breakdown medium. A high peak power wavelength conversion pulsed laser device, comprising: a collimator lens that returns light emitted from the breakdown medium to parallel light. 3. The high peak power wavelength conversion pulsed laser device according to claim 1, wherein the breakdown medium is at least air, N ₂ or He gas. 4. The high peak power wavelength conversion pulsed laser device according to claim 1, wherein the breakdown medium adjusts the breakdown intensity with respect to the pump laser light by at least the gas pressure. 5. The high peak power wavelength conversion pulsed laser device according to claim 1 or 2, wherein a spatial filter is arranged at a condensing point of the pump laser light in the breakdown medium.